We had our top mathematicians work on the formula for the perfect ugly Christmas sweater. Here's what they found. It appears that there is direct correlation between the number of reindeer featured in the sweater and how ugly the sweater is. This Adult Snow Drift Ugly Sweater uses these complex findings to create a hideous, yet strangely enticing look. It's smothered with the exact number of reindeer to create the perfect holiday look.